Abstract
By means of cineradiography and an Image analyzing system the authors analyzed, in 40 normal shoulders and 40 loose shoulders, the motion of the center of the humeral head and the instant center of the humerus to the glenoid between each 10-degree arc of motion during upward movement of the arm in the scapular plane. The results are as follows:
1. In normal shoulders, the motion of the center of the humeral head can be divided into two groups; one in the range between 0 and 60 degrees; the other between 90 and 150 degrees. The latter is distributed upwards and laterally in comparison with the former. All of the instant centers are distributed medially, that is, to the side of the glenoid, in comparison with those of the center of the humeral head.
2. In loose shoulders, the motion of the center of the humeral head can also be divided into two groups: one in the range between 10 and 80 degrees; the other between 100 and 150 degrees. The latter is distributed medially and downwards in comparison with the former. The motion of the instant center can also be divided into two groups: one in the range between 10 and 90 degrees; the other between 100 and 150 degrees. The former is distributed in the same area as in normal shoulders, but the latter is distributed laterally in comparison with all of the center of the humeral head. This result is different from that in normal shoulders.
3. Thus it was able to be shown that the motion of the glenohumeral joint in loose shoulders is abnormal between 100 and 150 degrees during upward movement of the arm in the scapular plane.
